1. Field of the Invention
The present invention relates to an injection hole member formed with an injection hole for injecting fluid and to a method for manufacturing the injection hole member. For instance, the present invention relates to an injection hole member of a fuel injection device and to a suitable method for manufacturing the injection hole member of the fuel injection device.
2. Description of Related Art
Conventionally, as disclosed in Japanese Patent Unexamined Publication No. 2002-102977 (patent document 1), an injection hole member formed with an injection hole provided by a taper hole is known. A central axis of the taper hole is inclined with respect to an axis of the injection hole member in its thickness direction, and the internal diameter of the taper hole increases from an upstream end toward a downstream end of the injection hole member.
In the patent document 1, the taper hole used as the injection hole is formed through punch press. Specifically, a taper punch, whose diameter decreases toward its tip end, is used. The tip end of the taper punch is driven into a base material of the injection hole member. Thus, the taper hole is formed along an outer peripheral surface of the taper punch.
The tip end of the taper punch is pressed against an end surface of the base material in order to form the taper hole in one time of the punch press. In this case, a distance between a pressing portion and a held portion of the taper punch is long. As a result, bending moment applied to the taper punch is increased and the taper punch becomes prone to break.
Therefore, as shown in FIG. 38A, a method of forming the taper hole with the use of a lead hole 2 formed in the base material 1 in advance can be employed. More specifically, the lead hole 2 is formed in the base material 1 in advance so that a central axis O of the lead hole 2 is inclined with respect to an axis T of the base material 1 in its thickness direction and the internal diameter of the taper hole 2 is substantially constant along its central axis O. Then, a taper punch 6 is driven into the base material 1 in a state in which a central axis P of the taper punch 6 is inclined substantially in the same direction as the central axis O of the lead hole 2. At that time, the taper hole is formed by widening the lead hole 2 with the taper punch 6. When the tip end of the taper punch 6 is entered into the lead hole 2, the taper punch 6 can press an edge of the opening of the lead hole 2 at a position closer to the held portion of the taper punch 6 than the tip end of the taper punch 6. Thus, the distance between the pressing portion and the held portion of the taper punch 6 is contracted. Therefore, the bending moment applied to the taper punch 6 is reduced compared to the case where the taper hole is formed in the one time of the punch press.
In the method shown in FIG. 38A, a line of intersection between a virtual plane Z, which is perpendicular to the central axis O of the lead hole 2 and the central axis P of the taper punch 6, and an inner peripheral surface 2a of the lead hole 2 is round in shape as shown in FIG. 38B. Meanwhile, another intersection line between the virtual plane Z and an outer peripheral surface 6a of the taper punch 6 is round in shape as shown in FIG. 38B. Therefore, an intersection line between a virtual plane H perpendicular to the axis T of the base material 1 in its thickness direction and the inner peripheral surface 2a of the lead hole 2 is elliptic in shape as shown in FIG. 38C. Meanwhile, another intersection line between the virtual plane H and the outer peripheral surface 6a of the taper punch 6 is elliptic in shape as shown in FIG. 38C. The ratio between a major axis and a minor axis of the former elliptic intersection line is substantially the same as the ratio between a major axis and a minor axis of the latter elliptic intersection line as shown in FIG. 38C. Therefore, in the early stage of the punch press, as shown in FIG. 38C, the taper punch 6 contacts the edge of the opening of the lead hole 2 at one point on a virtual plane L including the central axis O of the lead hole 2, the central axis P of the taper punch 6 and the thickness direction axis T of the base material 1. The contact at the one point inhibits the decrease of the bending moment applied to the taper punch 6. Therefore, the effect of preventing the breakage of the taper punch 6 cannot be improved.
Moreover, in the case where the taper hole is formed in the base material through the punch press, an area of the opening of the taper hole depends on a stroke of the punch in the pressing direction. A flow rate defined by the injection hole provided by the taper hole depends on the opening area of a smaller diameter opening of the taper hole. Accordingly, the flow rate defined by the injection hole will vary because of the variation in the opening area due to the punch stroke. As a result, injection quantity of the fluid will vary.
A technology for forming the injection hole in a plate-like injection hole member of a fluid injection valve in order to improve designing flexibility of the shape of the injection hole and the like is disclosed in Japanese Patent Unexamined Publication No. 2000-52157. In this technology, an axis of the injection hole is inclined with respect to a central axis of the injection hole member. A plurality of injection holes is formed in respective injection directions so that the plurality of injection holes is directed away from each other along respective injection directions.
In the injection hole member formed with the injection holes whose axes are inclined with respect to the central axis of the injection hole member, an injection angle of spray injected from the injection holes can be regulated if necessary. In the case where the spray is injected from the plurality of injection holes in one direction, a widening angle of the entire spray can be regulated by adjusting injection angles of the respective injection holes. In the case where the spray is injected from the plurality of injection holes in two directions, a widening angle between the two directions of the injected spray can be regulated by adjusting injection angles of the respective injection holes.
However, the injection angle can vary for each injection hole member because of deviation of an injection angle of the injection hole axis with respect to the central axis of the injection hole member, variation in the thickness of the injection hole member or the like.